1. Field of the Invention
The present invention relates to a method and an apparatus for fabricating a crystal fiber, and more particularly, to a method and an apparatus that an external electric field is applied on the grown crystal fiber during the growth procedure of the crystal fiber so as to induce micro-swing of the crystal fiber and form regions of reversed ferroelectric polarities.
2. Description of the Related Art
Ferroelectric materials, for example, lithium niobate (LiNbO3), lithium tantalate (LiTaO3) and potassium titanyl phosphate (KTP), are widely used in the manufacture of optical elements because of their high nonlinear coefficient and other excellent properties. One known example is that the technique of achieving quasi-phase matching (QPM) by periodically poling can effectively generate light with sum frequency generation (SFG), second harmonic generation (SHG) or difference frequency generation (DFG).
The procedure of creating regions of different polarization vectors is referred to in the art as “poling”. In the present, the relative successful periodically poled method is to define a periodical electrode on the ferroelectric material and provide a high-voltage electric field (about 20 to 28 kV/mm). The periodical electrode can be made on the metal film directly, or by covering a periodical photoresist layer on the metal electrode or between the electrolytic liquid. However, the above-mentioned poling techniques are accomplished after the growth of the ferroelectric material.
U.S. Pat. Nos. 5,504,616, 5,714,198 and 6,013,221 defined the desired periodical electrode by complicated semiconductor process to accomplish periodically poled domains. In order to accomplish periodically poled domains, an additional high-voltage electric field or an additional chemical process is needed according to the above-mentioned methods, and the poling procedure is accomplished after the growth of the crystalline material. Additionally, the periodically poled crystal fabricated by the semiconductor process is mostly bulk material that has the disadvantages of being difficult to match with the conventional fiber and of poor mode matching. Further, the waveguide structure material made by the above-mentioned methods also has the disadvantages of poor coupling efficiency with fiber and complicated fabrication process.
U.S. Pat. No. 5,171,400 disclosed a method including laser heated pedestal growth (LHPG) and heat modulation so as to fabricate a lithium niobate crystal fiber that has a domain period of 2.7 μm and a diameter of 500 μm. However, such crystal fiber has the disadvantages of large variation of diameter of the crystal fiber, uneven domain period and difficulty in controlling the manufacture conditions.
Consequently, there is an existing need for a novel and improved method and an apparatus for fabricating a crystal fiber to solve the above-mentioned problems.